Combine vinegar and salt in a saucepan(non-reactive - stainless steel, glass, ceramic) over high heat. Whisk until salt is dissolved. Transfer into bowl and whisk in the cold water. Refrigerate until ready to use
Fill two 1-quart jars with cucumbers. Add mustard seeds, garlic cloves, red pepper flakes, dill sprigs and sliced peppers dividing equally.
Pour chilled brine into jars divided equally.
Cover and refrigerate about 24 hours. Will last a month in the fridge, but mine have always lasted for several months. Use your own discretion.